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Fuel gauge

I have a 2001 Buick Lesabre with 130,000 miles on it. The fuel gauge will go to full when you fill it up but will flucuate back and forth between half and full. At times the gauge appeares to be accurate but then the next time you check the gauge when it have been at half full and will go to 3/4’s full. The car has a system that tells the miles driven and miles per gallon average. The average per gallon does not match what I have calculated the mileage to be by filling and dividing gallons used into miles driven. Do all cars have a fuel sender unit and if so would it be in the tank or outside of it. Any ideas what may be wrong?

Yes, you have a fuel sending unit and it is located in the gas tank. It most likely needs to be replaced.

Yes, all cars have a fuel level sender. It’s basically just a float in the tank that sends a signal to operate the fuel gage.

The odometer is taking its signal from the vehicle speed sensor, which measures the rotations of the tranny output shaft.

I don’t know what signals your computer is using to calculate the miles per gallon avaerage, but it sounds like it’s simply dividing the odometer signal by the estimated use based on the fuel level sensor signal.

If that’s true and the fuel level sender signal is flaky (as yours appears to be) then it’ll calculate useless and wandering outputs. Garbage in = garbage out.

By the way, your wandering level symptoms may be an indication of an intermittantly high-resistance connection from the fuel level sender. You could string a new line and see if the fuel gage symptoms disappear, even if you just do it as a diagnostic protocol.

Hawkeye, Have You Got A MInute?

GM put a lot of cars out there that developed problems with the fuel gauge sending units or “senders”. They are inside the tank and exposed to gasoline. Tiny metal fingers on the sender’s “wiper” disintegrate through a chemical reaction with sulfur in the gasoline. Then you get erratic readings like the ones you describe.

Ordinarily the fuel tank has to be dropped out of the bottom of the car to access the fuel pump/fuel gauge module on most cars. See if you can lift the lining in the bottom of your trunk. Between the spare wheel well and the rear seat back, on the trunk floor off to the right, look for a somewhat oval shaped plate held in place by six or eight screws. These plates are for accessing the module without dropping the tank. If you’ve got that set-up then you are fortunate.

You should have a technician verify that the problem is with the sender. Then the technician should be able to withdraw the pump/sender module and replace just the sender. Some people might tell you that you need the pump, too. However, the sender can be replaced as an individual part. I did one in my driveway and it wasn’t too bad. I used a video on You Tube and replaced just the “wiper”. Total cost for my DIY was less than $50. I would think a shop would probably be in the $150 to $300 range for the repair.

Look in your trunk and call for some estimates.


Thanks for the info. I’ll check out the trunk.